1. Field of the Invention
The present invention relates to an enzyme composition useful for binding food materials, and a process for producing bound food.
2. Discussion of the Background
A variety of methods have been used to bind food materials. One method which is widely used provides a frozen or heat-treated product in many cases. However, the binding strength of the glue used in many of the known processes has not necessarily been satisfactory, and it has been difficult to bind many materials with these glues.
In order to solve this problem, Japanese Laid-Open (Kokai) No. 284,867/1994 discloses a method in which food materials are bound by using a combination of a transglutaminase (hereinafter referred to as "TGase"), which is an enzyme, and caseins (including casein as well as caseinates such as sodium caseinate and calcium caseinate, and a casein partial hydrolyzate).
This method takes advantage of crosslinks between proteins produced by the TGase. In this method, caseins are used as a binder in combination with proteins present in food materials per se to enhance the binding strength. According to this method, a raw bound food, for example, raw restructured steak meat, can be produced without being frozen or heat-treated. In recent years, this method has been widely employed, not only in Japan, but also abroad as a method of producing bound food having a high commercial value.
A technique of producing low-calorie and low-salt bound food by adding TGase and caseins, such as a casein partial hydrolyzate, to animal meat and fish meat has also been investigated.
Methods of binding food materials without using TGase have been reported, and some of them have been put to practical use. For example, a method in which pieces of meat are bound using a combination of (1) a heat-coagulable protein, such as a wheat protein or the like and (2) an alkaline earth metal salt which produces an alkaline solution in water, such as calcium oxide, calcium hydroxide or the like, is disclosed in Japanese Laid-Open (Kokai) No. 268,665/1990. However, the bound food obtained by this method has a bitter taste and an undesirable proteinaceous smell. Accordingly, this method is not acceptable.
Further, it is well-known that myosin is eluted with sodium chloride and pieces of meat can be bound using gel-formability of the eluted myosin. However, since this method requires quite a large amount of sodium chloride, the food has a strong, salty taste. In addition, the salt content is high, which is undesirable for health reasons. Further, heating is required for binding the food. Accordingly, this method can only be used with certain types of food.
For the above-mentioned reasons, a method of binding food materials through the protein crosslinking reaction with TGase is preferable, Above all, the method disclosed in Japanese Laid-open (Kokai) No. 284,867/1994 is considered to be the best technique since bound food which is excellent in taste and flavor is produced.
It is also possible to produce bound food with TGase alone without using caseins, see Japanese 2.sup.nd publication (Koukoku) No. 55,116/1994. However, the use of TGase alone exhibits a binding strength which is inferior as compared to the combined use of TGase and caseins. Therefore, TGase and caseins provide the best results when they are used in combination. Consequently, caseins are considered in the art to be an essential component of an additive for producing bound food.
However, milk proteins cannot be used, in some cases, for producing processed food because of problems such as food allergies and the like. Especially, among milk proteins, caseins are known to cause food allergies. Further, in some foreign countries, the use of ingredients other than proteins derived from the food materials to be bound is legally controlled in accordance with the form of bound food. For example, in the Netherlands when producing processed beef steak meat, proteins derived from cattle meat, cattle bones or cattle skins can be used as a binder, but caseins derived from milk cannot.
Under such circumstances, a technique in which caseins are not used has been also studied. For example, WO 95/08274 discloses a method in which raw meat is bound by using a combination of TGase with an alkali metal phosphate and sodium chloride as a binder. However, in this method, it is indispensable to use, based on the weight of meat, 0.4% (weight %) or less of an alkali metal phosphate and as high as from 1.5 to 4% (weight %) of sodium chloride. Thus, a food product that loses the taste and flavor inherent in meat is produced.
Under these circumstances, a composition for binding food materials by which food materials such as pieces of meat or the like can be bound even in an unheated raw state without using caseins and a process for producing bound food having excellent taste and flavor have been in demand in the field of processed food.